The overall objective for this project is to gain an in-depth understanding of the importance of the binding of estrogens, androgens, and corticoids to plasma proteins. Specifically, we are engaged in the isolation of corticosteroid-binding globulin (CBG) from several species and the testosterone estradiol-binding globulin from man. The isolated proteins are being characterized as proteins per se in terms of their chemical and physical characteristics. In addition, detailed studies of their interactions with the steroids which they bind are being examined. In addition to these approaches we are examining the mechanisms by which the concentration in plasma of these proteins is controlled by various endocrine influences. Specifically, we are investigating, at this time, the influence of a host of hormonal factors on the level of hepatic mRNA which is responsible for the translation of CBG in the rat. Similar experiments are planned for the control of the testosterone binding protein of the rabbit.